Humidity sensing properties and respiratory behavior detection based on chitosan-halloysite nanotubes film coated QCM sensor combined with support vector machine

This work demonstrated an accurate and reliable quartz crystal microbalance (QCM) humidity sensor based on the chitosan-halloysite nanotubes (CS-HNTs) composite that can be used to monitor respiration lines. The hydrophilic polymer chitosan (CS) with halloysite nanotubes (HNTs) was characterized using SEM, TEM, XRD, XPS, FT-IR, and WCA investigations to analyze the microscopic morphology, molecular structure, chemical bond, and hydrophilicity. The experimental results showed that the QCM humidity sensor of CS-HNTs film demonstrated high sensitivity (69.1 Hz/% RH), superior humidity hysteresis (<2.8% RH), excellent long-term stability, repeatability, and outstanding selectivity. The subtle changes in fingertip movements and exhaled air humidity in different modes were detected by the QCM humidity sensor. A respiratory behavior monitoring model based on support vector machines was constructed to accurately determine five breathing modes and apply it to human breath detection and health medical diagnosis.